The isopentenyl isoflavone luteone as a pre-infectional antifungal agent in the genus Lupinus

The prenylated isoflavone luteone has been isolated from healthy leaves of Lupinus albus and 11 other lupin species. Evidence is presented that this compound occurs as a leaf surface constituent. In vitro tests indicate that luteone and a second unidentified isoflavone frorn L. albus possess antifungal activity sufficient to support their proposed role as pre-infectional resistance factors. No evidence was obtained to suggest that phytoalexins were produced by the fungus-infected leaves of L. albus.     

Fungal modification of pterocarpan phytoalexins from Melilotus alba and Trifolium pratense

Medicarpin (3-hydroxy-9-methoxypterocarpan), an isoflavonoid phytoalexin characteristic of sweetclover (Melilotus alba), is metabolised by three fungi, Botrytis cinerea, Colletotrichum lindemuthianum (race β) and C. coffeanum (isolates CCA and CCP) to afford products with decreased antifungal activity. Peterocarpan phytoalexins from red clover (Trifolium pratense) are similarly modified. A fourth organism, Helminthosporium carbonum apparently lacks this ability. Fungal-mediated tranformation principally involves hydroxylation, methylation and demethylation although ring fission has also been noted.     

Suppression of Meloidogyne chitwoodi with Sudangrass Cultivars as Green Manure

Meloidogyne chitwoodi race 1 reproduced on Piper sudangrass (Sorghum bicolor (L.) Moench), 332 (sudangrass hybrid), and P855F and P877F (sorghum-sudangrass hybrids), but failed to reproduce efficiently on Trudan 8, Trudex 9 (sudangrass hybrids), and Sordan 79, SS-222, and Bravo II (sorghum-sudangrass hybrids). Meloidogyne chitwoodi race 2 behaved similarly and reproduced more efficiently on Piper, P855F, and P877F than on Trudan 8, Trudex 9, or Sordan 79. The mean reproductive factor for M. chitwoodi races on the poorer hosts ranged from <0.1 to 0.9 under greenhouse and field conditions. Meloidogyne hapla failed to reproduce on any of the cultivars tested. In the laboratory, leaves of each cultivar chopped and incorporated as green manure reduced the M. chitwoodi population in infested soil more than unamended or wheat green manure treatments. Trudan 8, although limited to the zone of incorporation, protected this zone from colonization of upward migrating second stage juveniles (J2) for up to 6 weeks. Leaves of Trudan 8 but not roots were effective against M. chitwoodi, and J2 appeared to be more sensitive than egg masses. Trudan 8 and Sordan 79 as green manure reduced M. chitwoodi in bucket microplots under field conditions.